catkin_create_pkg error

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Hi , when i use catkin_create_pkg firstpackage std_msgs rospy roscpp , I get the following error message.

usage: catkin_create_pkg [-h] [-s [SYS_DEPS [SYS_DEPS ...]]] [-b [BOOST_COMPS [BOOST_COMPS ...]]] [-V PKG_VERSION] [-D DESCRIPTION] [-l LICENSE] [-a AUTHOR] [-m MAINTAINER] --rosdistro ROSDISTRO name [dependencies [dependencies ...]] catkin_create_pkg: error: argument --rosdistro is required

I am using ros hydro on ubuntu 13.04 and as i am a beginner , can someone please help me answer this question ? thanks in advance.